There are several variables available out of the box for use in running commands and scripts. Many of the variables prefixed with Sitecore derive from the Sitecore.config settings. Run the command Get-Variable to see the complete list available in the currently running session.
Variable
Example
AppPath
C:\Inetpub\wwwroot\Console\Website\
HostSettings
... FontSize : 12 FontFamily : Wingdings ...
me
sitecore\admin
PWD
master:\
PSScript
$PSScript.Appearance.Icon # Returns the icon of the executing script
Note: Any new variables created are stored within the current session; when the session ends the variables are removed. Be careful not to overwrite the built-in variables.